Abstract

Background

Approximately 20 % of patients diagnosed with breast cancer have also diabetes mellitus as a comorbid condition. There is growing evidence that the use of metformin in diabetic patients was associated with lower risks of cancer. In this study, we aimed to investigate retrospectively the demographic and clinicopathological characteristics of patients with different antidiabetics (AD) users at the time of breast cancer diagnosis.

Methods

From 3890 breast cancer patients who were taking AD drugs more than 12 months at the time of breast cancer diagnosis were enrolled (n = 378). Patients were classified as Group 1 if they treated only with metformin, Group 2; another oral AD, Group 3; oral AD combination, Group 4; insulin plus oral AD and Group 5; if they treated with insulin only.

Results

Median age of 378 patients diagnosed with breast cancer and diabetes was 58 (23-92). The median follow-up of patients was 47 months. There were 128 patients (%38.8) in Group 1, 106 patients (%32.1) in Group 2, 13 patients (%3.9) in Group 3, 27 patients (%8.2) in Group 4 and 56 patients (%17.0) in Group 5. The 5 groups were well-balanced and there were no apparent differences in histological type, terms of baseline tumor size, grade, axillary lymph node involvement, extracapsular extension, perineural invasion, lymphovascular invasion, type of surgery, menopausal status, HER2 positivity and hormonal receptor status between 5 groups. Both estrogen and progesteron receptor positivity were same between 5 groups. Treatment patterns such as hormonal treatment, chemothearpy and radiotherapy were also similar. Similarly, distribution of TNM stages were same between groups. 5-year DFS rates were 81.9%, 77.3%, 79.3%, 72.5% and 61.9% in Groups 1-5, respectively (P = 0.06). 5-year OS rates were 89.3%, 92.5%, 92.9%, 81.8% ve 67.7% in Groups 1-5, respectively. (P = 0. 002).

Conclusions

In our study, patients treated with insülin alone or combination have significantly worse OS and borderline significant worse DFS compared to diabetic breast cancer patients treated with oral AD medications. The insulin-sensitizing effect of metformin may play a major role in its anticancer activity. B